Heat exchanger



FIG. 1 is a top plan view of a heat exchanger, showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a side elevational view thereof;

FIG. 4 is a rear elevational view thereof;

FIG. 5 is a bottom plan view thereof;

FIG. 6 is an elevational view of the side opposite that shown in FIG. 3.

The conventional cord element has been shown fragmentarily in FIGS. 1, 2, 4, 5 and 6 for convenience of illustration. 

The ornamental design for a heat exchanger, as shown and described. 